Conventional fixed wrenches, whether of the spanner, box-end or the socket type that snap onto a square driver shaft, have the disadvantage that a large number of different sized wrenches or sockets are required to cover a working size range of hex fasteners. For example in the inch system, the range from ⅜ to ¾ inches (0.375″ to 0.750″) requires seven sockets in steps of 1/16″ or thirteen sockets in steps of 1/32″; and, in the numbered metric system, the range from 10 mm to 20 mm (0.394″ to 0.787″) requires eleven sockets in steps of 1 mm.
As substitutes for single or dual fixed spanner wrenches, adjustable spanners such as “monkey wrenches” and pipe wrenches have been well known and widely used for many years. However such adjustable spanners effectively engage only two of the six facets of hex fasteners and thus tend to fail and/or damage the fastener when high torque is required and applied, whereas box-end or socket wrenches engage all six facets of the hex fastener, distributing the torque and associated forces more evenly, and are thus capable of higher torque with less likelihood of failure or fastener damage.
As substitutes for single or dual fixed box-end wrenches, which engage all six facets of hex fasteners, socket wrench systems, wherein any of an assortment of sockets can be snapped onto the square end of a drive shaft driven by a ratchet handle, have become highly popular, especially to professional mechanics, for their convenience and versatility and are readily available either in individual pieces or in sets of various sizes required to accommodate a desired size range. However, the large number of pieces required is a disadvantage to many occasional users such as typical homeowners who may have only occasional need for a wrench but the required size is unpredictable.